1. Field of the Invention
The invention relates to a device for damping blade vibrations in turbo-machines.
2. Related Art
In turbo-machines, the rotating blades are excited, among other things, by irregular inlet flow. This exciting force often causes inadmissible alternating stresses in the blades. In order to combat these dangerous vibrations, an obvious method is to thicken the blade profile. This thickening does, however, cause a substantial deterioration in efficiency and it is therefore preferable to avoid this method in practice.
An arrangement which is frequently used, and has been in use for a long time, for combating the vibrations occurring, consists in connecting the blade aerofoils together in groups within a blading row by means of a damping wire.
This conventional arrangement does, however, have the following disadvantages:
The damping wire within the flow passage causes a deterioration in the efficiency of the turbo-machine. PA1 The damping wire is subjected to severe loads due to bending stresses and the temperature of the medium. PA1 The damping wire is subject to corrosion and erosion. PA1 Expensive machining and treatment of the contact surfaces. PA1 Expensive assembly. PA1 Varying contact surface forces depending on the operating condition. PA1 Mechanical wear of the contact surfaces so that the desired damping continually deteriorates.
The solution passage using damping wires outside the flow passage may be considered as the most recent innovation and this arrangement has been partially described in the ASME publication 81-DET-136. This type of design permits relative movement between the wire and the blades. Since the forces on the damping wire balance each other out due to the coupling of several blades, however, the friction is not fully utilised. The wire usually behaves excitation orders under control. In order to overcome these obvious difficulties, an attempt is made in the publication above mentioned to replace the damping wire with small damping pieces anchored to the rotor disk. However, such a solution cannot be accommodated in a practical design for space reasons.
Where the blades are designed with shrouds, the latter are used for damping, the flanks of the shroud plates being machined in such a way that they form common contact surfaces of various shapes. These shroud plate structures do, however, have various disadvantages: